Many advances in technology related to automatic litter boxes have arisen to help improve the cleanliness of the litter box. One of the most significant advances is the use of what's called the “sifting method” of filtering litter. The sifting method has been employed by such devices as described in U.S. Pat. Nos. 4,846,104; 4,120,264; 5,507,252 and 5,662,066 (see also U.S. Pat. No. 6,463,881). The sifting method is significantly more effective than the so-called “raking method” (or “combing method”) as described in U.S. Pat. No. 5,048,065. The sifting method of cleaning litter has two major advantages over the raking method in that it is far more resistant to clogging, and generally does a much better job of cleaning the litter. Gravity is used to separate the litter from waste material instead of forcing a rake through the litter to remove solid waste material. The major flaw with the raking method is that a motor forces not only the rake through litter, but also the solid waste material though the litter as well. Although the rake can be made in such a way to travel relatively easily through litter, the unpredictable shapes and generally large surface area of solid waste makes it difficult to force waste clumps through such a dense and heavy material such as clay litter. The typical behavior of cats to bury their clumps makes this process even more difficult.
There are often many undesirable effects with using such a raking method. One such effect is that clumps and other solid material can be wedged between the rack and the bottom of the litter pan, which can cause a smearing effect. The gradual build-up of such debris makes subsequent raking phases more and more difficult. Another such effect is that the mass of the litter itself helps to force litter clumps and other solid material in between the tines of the rake. In this scenario, gravity is actually hindering the filtering process. Because gravity is forcing the litter into the pan, the litter wants to stay where it is situated. As the rake and solid debris travel from one end of the litter pan to the other, the litter has to move out of the way of the debris, or be force to move in front of the debris itself and end up in the waste receptacle. The only way for the litter to get out of the way is to go above the debris, below the debris, or around the debris to either side. Gravity is always forcing the litter into the pan, and the litter that is forced to move out of the way of the debris is compressed against other litter within the litter pan. When the debris is close to the side of the litter pan, resistance is even greater. The options for which direction the litter can move are reduced, and further smearing can occur, and the increased force on the debris can further force the debris into the tines of the rake, clogging the rake. To compound the problem, it's common for cats to bury their waste into a corner, making a significant portion of the litter end up on one side of the litter pan. This makes it extremely difficult for the rake to filter the unevenly covered litter pan.
Because of these problems, there is usually a narrow range at which the litter must be maintained. Too little litter, and the clumps will stick to the bottom of the litter pan. To high a level, and the force required to push the rake and the debris through the litter is too great for the device to handle. Aside from a clogged rake making the litter box ineffective, it also increases stress on the mechanical parts, motor, and power consumption. It is also extremely difficult to unclog the rake, as well as being an extremely undesirable task to take on. U.S. Pat. No. 6,851,386 tries to address this problem by introducing a rake that is less susceptible to clogging; however the raking method itself cannot change the force of gravity working against the debris or the mass of the clay. Although significantly less clogging is achieved by this new rake design, the effect is that instead of clogging, the rake actually breaks up the clumps and/or other solid material into smaller pieces, traveling through the rake instead of into the waste receptacle where it is intended to be communicated. This results in an incomplete cleaning process. Clogging can also be reduced by increasing the angle on the tines of the rake to reduce the negative impact gravity has on the filtering process; although this improves the process, it does so only to a certain degree. Although the raking method has numerous disadvantages, it has the significant advantage in that an open litter box design is easily achievable. The importance of this feature will be described later.
The sifting method uses gravity to its advantage instead of to its disadvantage. Instead of moving relatively large masses of solid debris through dense clay litter, the sifting method uses gravity to make the litter move around the solid waste debris. The forces in effect are always relatively close to 1G, and no greater force than this is required to separate the solid material from the litter. The screen used to filter litter from solid waste material is therefore not subjected to the forces required by the raking method, and clogging is avoided. This method draws a parallel to the frequently demonstrated science experiment where a jar, a collection of small particles (e.g. sand), and a collection of larger particles (e.g. marbles) are provided. The sum volume of the small and large particles is such to approximate the volume of the jar. If the small particles are placed in the jar first, and then an attempt is made to place the larger particles in the jar, the effect of gravity on the small particles in the jar prevents them from moving out of the way to make room for the larger particles; however, by placing the larger objects in the jar first, and pouring the smaller particles in the jar second, the smaller particles will easily move around the larger objects, filling the jar with ease. This is another example of how gravity is used to help solve the problem, rather than hindering it from being solved. This principle is applied when the sifting method is employed, and provides a predictable, clog-free method of separating litter from solid waste material.
Many products today employ the sifting method. One of the more advanced products is described in U.S. Pat. No. 6,463,881, where a globe-like structure is used to house filtered litter, a sifting mechanism, and to provide a certain amount of room for an animal, as well as a hole through which the animal can ingress/egress the globe. This product is far superior in filtering litter than a product that utilizes the raking method, but is an enclosed unit which as certain disadvantages. Being an enclosed litter box, this product does have the advantage of making it far more difficult for the cat to throw litter outside of the litter box; however there are also significant disadvantages as well. The first and most important of which is that many cats simply will not use enclosed litter boxes. Secondly, this product must have ports in the globe that open to let waste exit the globe and fall into the waste receptacle. These ports limit the size of the clumps that can fit through these the ports, preventing the use of the device for cats that create large clumps; this particularly true for cats with diabetes, as the clumps will not fit through the ports. Thirdly, it is relatively difficult to introduce fresh litter into the globe as well as clean the globe (which is recommended to be done periodically). Furthermore, there are weight restrictions for cats that must be within a 5-15 lbs. range. A cat less than 5 lbs. will not weigh enough to trigger the sensor, and cats over 15 lbs. will have trouble fitting into the globe.
U.S. Pat. No. 5,167,204 attempts to use a rake-like structure, but through manual manipulation effectively employs a sifting mechanism. This has the significant advantage of using the sifting method while still providing a traditional open litter box that's attractive to the largest population of cats; however this mechanism has multiple disadvantages, the first of which is that the device would have to be very large in order to create a litter area large enough for a typical feline to use effectively. The second disadvantage is that the mechanism is not automated, and would be difficult to automate. The third disadvantage is that it is would be very difficult to level the litter without picking up the entire litter box and shaking it around.
The raking method does have a significant advantage in that the process itself is conducive to the traditional open litter box design. Although it's possible to place an enclosure around such a litter box to help contain litter, an enclosure is not required in order to make the litter box operate. A litter box is only effective if the cat will use the device, and because many cats will simply not uses enclosed litter boxes, a perfectly designed enclosed system will not do the job if the cat does not elect to use it. For those cats that will not use an enclosed device, the alternative is that the cat will either use an unenclosed litter box if available, or an undesirable location if not available. Even cats that will use an enclosed litter box will often prefer an unenclosed litter box if given the choice. This makes it even more difficult to get the value out of a potentially expensive enclosed litter box device if a pet owner has multiple cats. Even if only one cat within a multi-cat household will not use an enclosed litter box, it is often the expectation of the pet owner to reap the benefits of the enclosed device with the cats that will use the enclosed device, while for the cat or cats that will not use the enclosed device, deal with the added labor involved in maintaining the unenclosed device for those stubborn cats only. However, because many cats that would otherwise use the enclosed device if that were their only option will often use the unenclosed device when given the choice, the effectiveness of the enclosed device is further reduced, as it gets used even less frequently than expected by the cat owner.
The challenge is thus to create an automated litter box that has superior filtering capabilities by utilizing the sifting method, and yet has an open design to encourage use by as many household pets as possible. It is against this background and the need to solve these problems not addressed by prior art that the present invention was developed.